The invention relates to an alarm system with a sensing arrangement, such as a glass break sensor, which system is connected with a source of electric power transmitted between movable and fixed parts.
For the security of buildings, it is well known to monitor weak points such as windows, doors, and other possible break-in points with electromechanic and electronic sensors connected in alarm circuits. Sensing arrangements such as glass break sensors, shock recorders or similar alarm generators have been applied to the surfaces that are to be monitored and connected electrically with a center providing a signal or an alarm.
For making electric connection between two movable parts that are to be monitored, as, for example, a movable wing or sash of a window and a fixed window frame, it has been the usual practice to employ either movable cable jumpers or relatively movable electromechanical contacts. These arrangements, however, are frequently the cause of system breakdowns. Thus, cable jumpers tend to break because of mechanical loads or strains due to frequent opening and closing of windows, doors, etc., whereas electromechanic contacts are pitted or fouled for similar reasons. This results in failures to the alarm system due to broken or ineffective connections. The object of the present invention is to provide alarm systems of a type which do not require direct electrical contact in the electrical transmission system between the relatively movable parts.